1. Field of the Invention
The present invention relates to a synchronizing stage in a regenerative repeater at the receiving side of a transmission circuit for the acquisition of a synchronizing signal from a biternary data sequence for the synchronization of a clock generator in the regenerative repeater.
2. Description of the Prior Art
In digital transmission technology, lines, light waveguides and radio links are employed as transmission circuits for analog signals and data signals. A plurality of transmission circuits must be connected following one another for connnecting points which lie far apart, whereby the individual transmission circuits are connected by elements referred to as regenerative repeaters. The regenerative repeaters serve the purpose of regenerating the signal received on the incoming transmission circuit, in terms of shape, and amplifying the received signal to a predetermined signal intensity and outputting it to the outgoing transmission circuit.
Regenerative repeaters in radio link technology are known from the descriptive material for the radio link device FM7200 of the Siemens company.
It is generally standard to place the digital signals onto the transmission circuit with a limited bandwidth. Due to the band limitation, a binary or a biternary (binary coded ternary) data sequence arises at the receiving end of the transmission circuit dependent on the bit rate of a binary data sequence. Hereinbelow, that case in which the regenerative repeater receives a biternary data sequence via the transmission circuit shall be considered.
The binary data sequence alternately assumes four different amplitude values with reference to a zero line. These are a maximum positive and a maximum negative amplitude value, and a positive and a negative amplitude value. The two latter values are noticeably lower in amplitude than the maximum positive or, respectively, maximum negative amplitude value. Biternary data sequence comprises long and short signal edges, whereby along signal edge connects a maximum and a minimum amplitude value to one another and a short signal edge connects a maximum positive or, respectively, maximum negative amplitude value to a negative or, respectively, positive amplitude value. The steepness of these signal edges is dependent on the bit rate of the biternary data sequence.
The signal edges of the biternary data sequence are jittered due to the attenuation on the transmission circuit, i.e. they do not form a narrow line, but a spread line when, for example, displayed on an oscilloscope. In order to be able to regenerate the original binary data sequence in the regenerative repeater from the received, biternary data sequence, the bit clock must be recovered from the incoming biternary data sequence.
It is conceivable to sample the biternary data sequence on its zero line and thereby acquire synchronizing pulses for regenerating the bit clock. This method supplies a nearly accurate result given long signal edges of the biternary data sequence but does not supply this result in the case of the short signal edges. These, in particular, are greatly jittered infested. It is also conceivable to sample the biternary data sequence with threshold amplifiers whose thresholds lie approximately in the middle between the maximum positive amplitude value or, respectively, the maximum negative amplitude value and the zero line. In both cases, the results are inaccurate since, as already stated, the signal edges are dependent on the form of the binary data sequence, i.e. on the data stream.